1. Field of the Invention
The present invention relates to non-volatile memory devices, and more specifically to a programmable non-volatile memory device having additional rows of memory cells that can be reprogrammed to modify the stored data stored.
2. Description of Related Art
FIG. 1 is a block diagram of a conventional programmable non-volatile memory device. The device includes a matrix 1 having non-volatile memory cells (or permanent memory points) organized into rows and columns. Generally, the number of columns corresponds to the number of bits that are stored for each data word, and the number of rows is greater than the number of rows required for storing all data words (i.e., the number of addresses or addressable words in the memory). For example, the non-volatile memory device of FIG. 1 holds m data words and has m+n rows in the memory cell matrix 1. Such a non-volatile memory point structure is typically formed by fusible elements that cannot revert back to an inactive state after being programmed into an active state. Thus, the n additional (or redundant) rows of memory cells allow for limited non-volatile reprogramming of the memory device.
The memory cell matrix 1 is associated with a row addressing circuit 2 that decodes and routes row addresses received from an address bus A. In other words, the row addressing circuit 2 selects a row of memory cells based on the address received at the input of the memory device. Additionally, the memory cell matrix 1 is associated with a read/write amplifier circuit 3 that receives and outputs data D typically having a number of bits equal to the number of columns. In practical memory devices, the row addressing circuit forms an array of switches for routing the outputs of an address decoder to the m word lines so as to select a row of memory cells in the matrix 1. Each row of the matrix 1 can only be programmed once, and the n additional rows are provided to allow a non-volatile reprogramming of rows of the memory matrix. Thus, in the memory device of FIG. 1, there are n possibilities for memory reprogramming and then the non-volatile memory device becomes non-programmable (i.e., read-only).